Rotating rigid disk magnetic storage devices (sometimes referred to as "drives") typically utilize data transducers which fly upon an air cushion immediately adjacent to the storage surface. The transducer is held just above the surface by an air bearing effect.
In disk drives employing such technology the data transducers are supported by a carriage assembly which is normally biased to position the transducers at a predetermined landing zone on the disk storage surface. In some cases the landing zone is located inside the innermost annular data storage track of the storage surface. In some cases, the driving mechanism may be a linear translator such as a linear voice coil solenoid. In other cases the driver may be a stepper motor or a rotary actuator. In any event, when power is removed, or when the storage disks are not rotating at their normal operating speed, the back EMF of the rotational motor powers the heads to a landing zone where the latch holds them.
The disk storage surface is typically coated with a very thin magnetic material which stores the recorded data for later retrieval and/or replacement. The storage surface is packed with very high data densities, on the order of 10,000,000 bits or more per inch. The storage surface is particularly sensitive to being damaged. Any minute scratch or indentation may deform the storage surface, with resultant loss of data and data storage capability at the damage site.
The movement of a data transducer across the recording surface in the absence of the air bearing or cushion may result in damage to the storage surface from minute scratches or dents. The damage or deformity is caused because of a loading force provided to the transducer to urge it against the disk surface. The loading force is opposed to the force generated by the air bearing effect. The loading force is provided with a value which causes the transducer to come within 1 to 2 microinches of the storage surface during operation.
When the drive is not in operation, the loading force applied to the transducer may be sufficient to dent or gouge the storage surface in the absence of the protective air cushion. Also, the storage surfaces may be dented if the transducers are susceptible to severe, complex rotational and/or translational forces sometimes encountered during unusually rough shipping and handling. As disk drives become smaller, and as they move through commerce by common carriers unaccustomed to handling delicate instruments, such drives have become susceptible to storage surface damage arising from severe handling.
The most common damage sustained by severe handling has been denting of the storage surface. Such dents are caused by severe shock forces having substantial components normal to the parallel planes of the disk surfaces. As already mentioned, such dents are known to prevent the drive from storing data at the locations thereof. If such dents occur during shipment and/or handling between the factory and the user, their presence will go undetected until data storage errors are encountered by the user.
The requirement to lock the data transducer assembly of a rotating rigid disk data storage device during shipment and handling is recognized in the prior art. There are three general approaches: mechanical locking devices; solenoid safety latches which are disengaged only when the drive is in operation; and, permanent magnet latches which lock the assembly against movement in response to shocks below a threshold force level.
Mechanical latches come in many forms. One is an air-driven device (see U.S. Pat. No. 4,979,062) which uses air currents generated by the moving disc. Another is a counter rotating device that is activated by shocks and is spring loaded. Both types work most of the time. Solenoids are usually effective (see U.S. Pat. No. 5,216,682; 4,965,684; 5,694,271), but they add additional cost and power consumption overhead. Permanent magnets are only partially effective (see U.S. Pat. No. 5,170,300 and 5,452,159). They have the drawback that very severe shocks to the drive may overcome the locking force, leading directly to the infliction of the damage sought to be avoided.
One drawback of disk drives is that the unit must be assembled and operated in a very clean, dust free environment. Once assembled, the drive is enclosed within a hermetically sealed housing to protect against intrusion of unfiltered ambient air. This ultra-clean environment renders impractical the use of temporary, removable locking members or devices to manually lock the actuator assembly within the disk drive enclosure.
A need has therefore arisen to provide a more satisfactory locking mechanism which will lock the data transducer assembly at a safe position whenever severe mechanical forces or shocks might be encountered, and which will release to enable normal operation of the drive when the storage disks are rotating.